In general, there are two types of optical fibers. One type comprises a core material of uniform refractive index surrounded by a cladding having lower refractive index. The other type is a graded index fiber comprising a material wherein the refractive index tapers off from a maximum value at the center to a minimum value at the outer surface.
When using such optical fibers in an optical transmission line connecting an optical signal source to an optical signal receiver, it is important to connect the optical fibers with a precise alignment and, accordingly, with a low optical power loss at the point of connection.
If each of the two end surfaces of two optical fibers to be connected is perpendicular to the central axis thereof and, furthermore, has a precise flatness and purity, then the connection of these optical fibers can be easily realized with a low optical power loss by merely directly aligning the two end surfaces.
It is generally the case, however, that the central axes of the optical fibers tend to become deflected and inclined at the point of connection and that the deflection and inclination causes an increase in the optical power loss at the point of connection.
Conventional optical fiber connectors for connecting two optical fibers with a precise alignment do exist, but all of these conventional optical fiber connectors require particularly fine adjustment for precise alignment or positioning, and furthermore, require highly precise machining, highly skilled techniques in the connection of the optical fibers and so on. As such, conventional connectors are not considered to be of a practical or useful nature as their operation is complicated and requires much time.
For instance, the methods of fixing the two end surfaces of the optical fibers with adhesives, welding the two end surfaces, and so on, require the use of a precise three-dimensional fine adjustment microscope and so on in order to decrease the axial deflection and inclination of the optical fibers. Thus, these methods require operations which are so complicated that they do not have any pratical value.
There is yet another method of connecting optical fibers, which consists of forming a groove corresponding to the shape of the optical fibers in a plate made of plastic material, arranging the optical fibers into the groove and holding them fixed with a holding plate therein, but this method also requires so many operations and so much time that is can never be deemed to be of useful or practical value.